Mercury Levels in Biota and Sediments of Princess Royal Harbour, Albany, Western Australia: Interpretation and Management Implications
Keywords:Receiving water regime, seagrass, inorganic sediments, detritus, Hg standard. Hg discharge, fertilizer, superphosphate, coastal water
A minor Hg discharge (14.2 kgHgyr -1) over 30yr to Princess Royal Harbour resulted in Hg levels in the edible flesh offish to range 0.01 to 7.6 mg/kg-1 wet wt with high values occurring in carnivorous species. Hg levels in cockles (all soft tissues) ranged 2.2 to 50 mg/kg-1 wet wt. These values are moderately high and exceed the Australian health standard of 0.5 mgHgkg-1 wet wt for foodstuffs. (The contaminated part of the harbour has been closed to fishing). Levels in sediments are low by world-wide comparison, with a maximum value of 2.2 mg/kg-1 dry wt found in fine detritus-rich surface sediment in a seagrass meadow at a considerable distance from the outfalls. Those in quartz-rich (sand) sediments around the outfalls are very low, ranging 0.04-0.11 mg/kg-1 dry wt, indicating little affinity for Hg. Whilst flushing is good (14 days) and water velocities reach 0.5ms -1, lack of turbulence allows buildup of Hg-contaminated detritus in seagrass meadows, which act as a natural particulate trap in addition to adsorbing Hg. Hg accumulation up the food chain is probably due to contaminated seagrass/detritus acting as a fish nursery and food source for both fish and benthic organisms which they predicate. Results are discussed in terms of remedial action and natural value of the contaminated area, suitability of health standards and discharge management. Because export of contaminated particulates and detritus is low, the problem may remain for some time. Hg discharge to seagrass meadows and organic-rich sediments should not occur, regardless of flushing rates and water velocities. Given the high Hg levels in larger marine species around Australia, Hg discharge to coastal waters should be generally avoided.